A safety means of this kind is known from U.S. Pat. No. 4,036,144. The specification teaches an arming rotor that has a plurality of half-shafts, each of which is intended to be rotated about its axis in a first rotational direction by means of a motor provided herefor, to a position in which the rotor is free to rotate. If no torque is applied to the rotor in conjunction herewith, each half-shaft is rotated by a spring in the opposite direction, to a position in which the rotor is again in a safe position.
Thus, with this known safety means the half-shaft is moved to its armed position and back to its safe position with the aid of two mutually different drive devices, each of which drives the half-shaft in a mutually opposite direction. This renders the construction of the known arrangement complicated and also increases the risk of a malfunction.
The U.S. Pat. No. 3,170,404 teaches a further safety means of this kind, in which an arming rotor is normally locked through the engagement of a half-shaft in a recess located in the rotor. In order to release the rotor, it is necessary to rotate the half-shaft out of engagement with the recess, to the aforesaid safe position of the rotor, and also to rotate the half-shaft about its axis at a predetermined speed. If, in the other hand, the half-shaft moves with excessive speed, i.e. rushes, there is sufficient time for the half-shaft to re-enter the recess in the rotor so as to prevent the rotor from rotating, i.e. to restore the rotor in its safe position. With this arrangement, however, there is the risk that the rotor, if biassed, may have time to rotate slightly before the quickly moving half-shaft is able to enter the recess thereby preventing the rotor from being restored to its safe position.